The maintenance of human bronchus and pancreatic duct in a controlled experimental setting provides an excellent in vitro system to study the metabolism of chemical carcinogens including those found in tobacco smoke and in the environment. Cultured human bronchus can metabolically activate several classes of chemical carcinogens e.g., polynuclear aromatic hydrocarbons, acyclic and cyclic N-nitrosamines, hydrazines and mycotoxins. The pathway of benzo(a)pyrene (BP) metabolism leading to the binding (-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrohydrobenzo(a)pyrene to DNA has been defined in cultured human bronchial mucosa. The major BP-DNA adduct is between the 10-position of BP and the 2-amino group of guanine. Therefore, the metabolic pathway forming the predominant BP-DNA adduct in human bronchus is similar to that found in experimental animals in which BP is carcinogenic. A 75-fold variation among individuals in the binding of BP to DNA in cultured bronchi has been measured. Nontumorous bronchi from patients with epidermoid carcinomas of the lung bind significantly more BP to DNA than specimens from patients with either no cancer or adenocarcinoma of the lung. BIBLIOGRAPHIC REFERENCES: Harris, C., Autrup, H., Connor, R., Barrett, L., McDowell, E., Trump, B.: Interindividual variation in binding of benzo(a)pyrene to DNA in cultured human bronchi. Science 194: 1067-1069, 1976. Yang, S.F., Gelboin, H.V., Trump, B.F., Autrup, H., Harris, C.C.: Metabolic activation of DNA binding of benzo(a)pyrene in cultured human bronchus. Cancer Res. 37: 1210-1215, 1977.